With the continued concern over global climate change there is an increasing need to develop technologies to replace those with high ozone depletion potential (ODP) and high global warming potential (GWP). Though hydrofluorocarbons (HFC), being non-ozone depleting compounds, have been identified as alternative blowing agents to chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) in the production of thermoplastic foams, they still tend to have significant GWP.
Hydrofloroolefins, such as HFO-1243zf, (cis/trans)-HFO-1234ze, HFO-1234yf, and (E/Z)-HFO-1225ye, have been identified as potential low GWP blowing agents for the production of thermoplastic foams, including extruded polystyrene foams for thermal insulation.
It was discovered that blowing agent compositions comprising a tetrafluoropropene and at least one co-blowing agent selected from carbon dioxide, water, alkanes and an alcohol can permit the production of lower density, closed-cell foam with good long term R value which will be particularly useful for thermal insulating foams. This invention may also permit the production of low density, closed-cell foams with enlarged, controlled cell size.
WO 2004/037913, WO 2007/002703, and US Pat. Publication 2004119047 disclose blowing agents comprising halogenated alkenes of generic formula that would include numerous HFOs and HCFOs, among many other materials including brominated and iodinated compounds. Specific examples are shown for blowing agent compositions for foaming polystyrene comprising HFOs, specifically HFO-1234ze and HFO-1234yf, either alone or in combination with an HFC, and blowing agent compositions for PUR foaming comprising HCFO-1233zd.
GB 950,876 discloses a process for the production of polyurethane foams. It discloses that any suitable halogenated saturated or unsaturated hydrocarbon having a boiling point below 150° C., preferably below 50° C., can be used as the blowing agent. Trichlorofluoroethene, chlorotrifluoroethene, and 1,1-dichloro-2,2-difluoroethene are disclosed in a list of suitable blowing agents along with 3,3,3-trifluoropropene.
CA 2016328 discloses a process for preparing closed-cell, polyisocyanate foam. Disclosed are organic compound blowing agents including halogenated alkanes and alkenes, where the alkene is propylene, and the halogenated hydrocarbons can be chlorofluorocarbons. Among the many exemplary compounds listed are specific chlorofluoroethylenes containing 1 chlorine and from 1 to 3 fluorines along with specific pentafluoropropene, tetrafluoropropene, and difluoropropene.
US 2008/135800 discloses the use of HFO-1234ze as blowing agent for polystyrene foaming. Blowing agent compositions shown in examples include: 100% trans-HFO-1234ze, 50 wt % trans-HFO-1234ze and 50 wt % HFC-245fa, and 80 wt % HFO-1234ze and 20 wt % HFC-245fa. Of the polystyrene foam examples shown using 1234ze in the blowing agent formulation, the lowest density produced was about 5 pcf. The patent application discloses that water, CO2, and alcohols can be used as coblowing agents and claims various composition ranges that these coblowing agents could be used (eg. 10% to 20% water, etc).
In the production of insulating foam it is desired to have low density foamed products that maintain a high, long term R-value (insulating value). Though HFC-134a can provide long term R-value it is not soluble enough in polystyrene to produce foam product to the same low density as with using HCFC-142b or CFC-12. HFC-134a also has a very high nucleation density such that foams produced with it tend to have a very fine cell structure, which is not desired in all applications. HFC-152a and HFC-32 can be used to produce lower density foams with larger cell sizes than with HFC-134a but their high diffusivities in polystyrene will result in foams that age faster and don't possess the same long term R-value.